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UNITED STATES PATENT OFFICEo GEORGE M. MOWBRAY, OF NOR-TH ADAMS, MASSACHUSETTS, ASSIGNOR TO THE AMERICAN ZYLONITE COMPANY, OF NE\V YORK, N. Y.

MANUFACTURE OF PYROXYLINE.

SPECIFICATION forming part of Letters Patent No. 350,497, dated October 12, 1886.

Application filed January 27, 1886. Serial No. 189,968. (No specimens.)

To all whom it may concern.-

Be it known that I, GEORGE M. DIOWBRAY, a citizen of the United States, residing at North Adams, in the county of Berkshire and State of Massachusetts, have invented new and useful Improvements in Manufacture'of Pyroxyline, of which the following is a specification.

The generic term pyroxyline has been ap plied to three several combinations of cellulose I J with nitric acid, viz: First, trinitro-cellulose or gun-cotton; second, dinitro cellulose or soluble pyroxyline, used by photographers; and, third, mononitro cellulose or Xyloidine. Variations of temperature and of the strength of the nitric. acid or mixtures of nitric and sulphuric acid used for the acid bath in which the cellulose is immersed cause variations of the product; hence manufacturers who aim to produce dinitro-cellulose of uniform quality are'very conservative in venturing on change of process lest certain properties which render it useful to form zylouite or celluloid, &c., plastic compounds capable of being molded by heat and pressure should be affected to their detriment. Further, the hygroscopic properties of fibrous cellulose in the form of tissue-paper and bleached cotton. offering so large a surface to moist air, and the absorption of aqueous vapor from the atmosphere by 0- the acids used weakens the acid bath, and thus vary the quality of the product, these varia' tions of quality being accompanied by a diminution of the quantity yielded under these variable conditions.

Apart from the specified strength of the acids stated hereinafter,which are given as being especially suited for making soluble pyroxyline, the process and apparatus herein described are likewise adapted for the manu- 0 facture of gun-cotton and Xyloidine.

In manufacturing soluble pyroxyline the method practiced heretofore has been, to prepare a standard mixture of nitric and sulphuric acids to serve as an acid bath in which is 5 immersed some form of cellulose-such as fine tissue -paper, bleached cotton, ramie fiber, &c.after immersion for half an hour, more or less, the cellulose having been converted .into nitrocellulose, it was lifted out of the acid bath, and the adhering spent acid amount 5:) ing to nearly onefourth of the original bath, was in part removed by means of a centrifugal machine, and the nitrocellulose plunged beneath water and washed until all traces of acid were removed. The acid bath was then replenished from the standard mixture of nitric and sulphuric acids and immersion of cellulose repeated, as before. The acid removed by the centrifugal machine, termed spent acid, was treated as a by-product, 6o being usually returned to the chemical works, and there credited at about one-fourth of its original cost, exclusive of labor, handling, repacking, shipping, transportation, breakage of carboys, &c. It would seem that the acid separated from the nitro-cellulose by the centrifugal machine was supposed to differ from that left in the converting vessel, and the fact that they are identical, if not overlooked, was disregarded. Meanwhile this spent acid accumulated at a rate of from fifteen to twenty kilos for each kilo of nitro-cellulose produced; but the most serious defect of this mode of nitration lies in the step-by-step weakening of the converting-bath at each and everyimmer- 7 5 sion with the inevitable conseqence that the product of the first imIIlGlSlOll differed in quality from each subsequent immersion, the percentage increase of weight diminishing in proportion and giving rise to the observation that no two batches of pyroxyline were alike. Owing to this unsatisfactory state of the process from time to time the acid in the converting-pots was emptied out and returned to the chemical works as spent acid. Some 8 manufacturers erected settling-tanks, devised processes of filtration or precipitation, and having accummlated a large quantity subjected it to analysis and corrected its defects. My improvements secure uniform quality of product, greater yield, using spent acid over and over again until consumed, the labor, cost, and time in clarification, filtration, settling, 800., is avoided. Onefourth the stock of acids on hand suffices to supply a factory, as compared with former methods. I will describe these improvements, referring to my applica tion (Case C) filed of even date herewith for the details of the apparatus, and simply enumerate them in this application: first, a turntable mounted with eight converting-vessels, each having a capacity of thirty gallons, more or less; second, a centrifugal machine; third, a spent acid tank; fourth, a concentrated mixed-acids tank; fifth, a building-up acidtank with appliances; sixth, a temperaturecontrolling coil; seventh, a dumping-trough with water-supply, drainage, &c.; eighth, a washing-tank with purewat'er supply, drainage, &c.

Gages to acid-cylinders, air-supply at a pressure of about twenty pounds to the square inch, and all necessary appliances will be found figured and described in said application 0. Into each of the eight converting-vessels I enter one hundred and fifty kilos of normal standard mixed acid for making soluble pyroxyline consisting of- H,SO,, 65.00 per cent., or thereabout.

HNO,, 17.78 per cent., or thereabout.

H.,O, 17.22 per cent-., or thereabout.

A convenient charge of cellulose (fine tissue-paper, bleached cotton-yarn or bleached ramie, 8:0.) is one kilo and three hundred and twenty-five grams to the one hundred and fifty kilos of acid, and time of immersion suitable twentyifour and onehalf minutes, more or less; temperature of acid Fahrenheit, which is attained by passing acid through tempering-coil. Varming and cooling the contents of the eonvertingvcsscls directly by the old method of immersing a copper worm connected to a steam-hose or by running a stream of ice-water through said coil interferes with nitration, besides risk of steam or water escaping into the mixed acid.

The composition of the concentrated mixed acids used by me in manufacturing soluble pyroxline is as follows:

H.,SO,, from 58.20 to 05.00 per cent. HNO,, from 38.80 to 32.00 per cent. H,O, from 3.00 to 3.00 per cent.

100.00 100.00 These acids are weighed in the iron drums and forced direct from the drums by conipressed air iuto the concentrated mixed acids tank.

The building-up acid, serving to refill the convertingvessels after each immersion, is composed as follows: Concentrated mixed acids, one part, by volume, equals two hundred and fifty-six pounds, by weight. Spent acid from centrifugal, five parts, by volume, equals twelve hundred and sixty pounds, by weight. The building-up acid tank should be of large capacity, so as to contain two days supply, if necessary, or, better, there should be two of these tanks, so that a days supplymay always be ready a day beforehand. This renders night labor or overtime work unnecessary, always a source of dissatisfaction to employer and employed. A convenient proportion of cellulose in the form of strips of tissue-paper I have foundto be thirteen hundred and twenty-five grams, to be immersed in one hundred and fifty kilos of normal standard mixed acid and warmed to 85 Fahrenheit.

Each converting-vessel is charged in manner as follows: The cellulose being entered into each vessel of acid at intervals of three .and one-half minutes, so that by the time the firstcharged vessel arrives at the ,centrifugal machine the eighth vessel will have received its charge, and twenty four and one -l1alf minutes will have been occupied, a period that has proved sufficient for conversion with thin tissue-paper. The nitro-cellnlose is now rapidly transferred from the converting-vessel to the centrifugal maehiue,which in two or three minutes separates about thirty-two kilos of spent acid,tlowing by gravity to the spentacid tank. The rinsed nitrocellulose, which persistently retains from six to seven kilos averaging 6.4 kilos-is next plunged beneath water in the dumping-tank, whence it passes into the washing-tank. On an average each converting-vessel will be found to lose 38.4 kilos, while the total contents of the vessel have deteriorated in strength. By the old method this deficiency, amounting toabout thirty-eight kilos, was replenished with nor.- mal-standard mixed acid,leaving one hundred and twelve kilos of spent acid in each converting-vessel unfortilied,and,as this omission was repeated twenty-five times in each vessel every working-day, we can now understand how it was that it was current remark no two batches ofpyroxyline were alike. In fact, each days product was made up of various qualities.

My improvement, in lieu of using the normal-standard mixed acid to replenish the convetting-vessels and rejecting more or less of the spent acid from the centri t" ugal machine,substitutes what I term a bnildingup acid, which includes all the spent acid of the previous days working fortified with concentrated mixed acid, and, as proven by months of consecutive work, observes the following conditions and limitations: First, reserves all the spent acid separated by the centrifugal mach i 11c today for the next days work; second, the volume of concentrated nitric and sulphuric acidsadded does not exceed the volume ofspcnt acid sub tracted and lost in the washing-water; third, the concentrated nitric and sulphuric acids contain not merelythe same equivalents as a like volume of normal-standard mixed acid, but, in addition, enough nitric acid to replace that which has been consumed in nitrating thirteen hundred and twenty-five grams of cellulose, also what is lost in fumes by evaporation during conversion and in the centrifugal process; fourth, the degree of concentration of the new acids used with the spent acid is such as to take up the water formed both by the chemical reaction and by absorption from the atmosphere during the twenty-four minutes necessary for conversion; fifth,the building-up acid is not so concentrated nor so different from the normal-standard mixed acid that if accidentally an over supply or an un der supply should reach a converting-vessel the product would be seriously affected. These five conditions and limitations of my invention during consecutive work on alarge scale have been observed with the result of producing soluble pyroxyline of uniform quality,and without perceptible deterioration of the acid bath.

The arrangement of eight convertingvessels, one centrifugal machine, and one dumping-trough of water, since I charge a converter every three and a half minutes, has the effect that eight three-and-half-minute intervals occur between immersion and removal, or a period of about twenty-four and one half minutes is allowed for converting the cellulose into nitro-cellulose. Meanwhile there takes place at every intermission of three and a half minutesviz.,an immersion of thirteen hundred and twenty-five grams of cellulose a removal of nitrocellulose to centrifugal basket, and thence to water; flow of about thirtytwo kilos of spent acid to spe1it-acicltank,and replenishing the converter with 38.4 kilos of building-up acid, ready for next series of immersions, &c.

I am aware of Patents No. 251,938, January3=1SS2, and No. 274,335, March 20, 1883, wherein the process of clarifying the residual acid, then ascertainiug'by analysis the constituents thereof, precedes restoration, it being alleged in said patents these acids cannot be used again with satisfactory results unless the matter in suspension, assumed to be flock detached from the fiber during treatment, be first separated. This flock, so called, being ferric sulphate, Fe.,(SO,),, as it disappears in the wasliingwater, and in no wise interferes with nitration, I disregard, thus saving from thirty-six to seventy hours time and precipitant. I also dispense with analysis, the process itselfbeing elastic enough to control the resultant product should that product, itself the best of tests, indicate variation of quality. I disclaim, therefore, settling, clarification, separation of flock, and analysis of residual acids preceding restora tion.

My invention, without stopping to analyze, or clarify, or estimate, or weigh, provides for uniform nitration. As a necessary consequence, the deterioration of the residual acids is uniform, and it follows their restoration can be defined with precision. It only remains to trace the converting-acid through the process of nitration to its final destination, viz: the greater portion, nearly threefourths, re mains in the nitrating-vessel. About fivesixths of the remaining fourth is separated by the centrifugal machine from the aciddripping nitrocellulose, whence it passes into the spent-acid tank, while the remaining onesixth of said one-fourth, persistently adhering to the nitro-cellulose during centrifugal action, is lost in the washingwater when the nitro cellulose is plunged into the washing-trough. To restore, we force up the contents of the spentacid tank into the bnilding-up-acid tank, and note how many inches of level it has reached, as shown by the glass gage. Ve will suppose forty inches. Ve now direct from the concentrated-acid mixture enough 'of said concentrated mixed acid to further.

raise the level of the acid in the building-up acid tank from seven to eight inches higher say until the glass gage marks forty seven or eight inches. As soon as a charge of aciddripping nitro-ccllulose has been transferred from a nitrating-vessel to the centrifugal ma- Chin the turntable is moved so as to bring the converting-vessel, from which the nitrocellulose has been removed, beneath the stopcock connected with the building up acids tank, the stop-cock is opened, and a volume of this buildingup acid equal to that removed with the rinsed nitro-cellulose is permitted to flow into the converting-vessel until the normal level that indicates a content of one hundred and fifty kilos is reached. Thereupon the supply is shut off. In fact,

about one twenty-fourth of concentrated mixed acid, by volume, or kilos 6.4, by weight, to gether with a volume of spent acid equal to that removed by the centrifugal machine from one batch of nitro-cellulose equal to thirty-two kilos, has practically restored the spent acid (kilos 111.6) left in the convertingvessel to its original strength and volume of one hundred and fifty kilos. It is now in condition to nitrate another batch of thirteen hundred and twenty-five grams of cellnlose.

I do not limit rnyselfto the precise weights or volumes mentioned in the above specification, as they may be varied slightly; nor do I limit myself to the exact proportions of tissuepaper or other form of cellulose to the normal mixed acid, it being desirable to increase slightly the quantity of nitric acid when the atmosphere is saturated with moisture in the summer months, and diminish slightly the proportion of nitric acid in the winter. The product itself is an unerring guide to an operator skilled in the art, requiring more building-up acid when the converted cellulose appears ragged, soft, or burned through, technically termed as being cut, and less buildingup acid when it is found on washing and drying to be imperfectly dissolved in a solution consisting of one part of camphor to ten parts of aleohol.

Having thus described my invention,what I claim is As an improvement in the art of manul facturing nitrocellulose, the within-described In testimony whereof I afiix my signature in process of restoring the spent acid of the presence of two witnesses.

nitrating bath in strength and bulk without precipitation and analysis by fortifying and GEORGE M. WOBRAY.

5 adding to the drained spent acid of a previous nitration a mixture of concentrated Witnesses: sulphuric and nitric acids, in the manner and HARRY S. MOWBRAY, about in the proportions herein set forth. MER ITT T. XVHITE. 

